Proteins, dipeptide and polypeptide (hereinafter collectively referred to as proteins) are responsible for most of the activities of a cell, such as catalysis, communication, defense, movement, and transport.
Proteins can be delivered to animals for the purpose of activating or supplementing a biological activity. Examples include antigens that activate an immune response and hormones that regulate growth and development.
The bases of a protein's biological activity is its sequence and/or conformation. Hence, the biologically active portion (such as an epitome) should remain essentially intact until it reaches its target destination. Factors that could limit the biological activity of a protein include chemical and enzymatic denaturation, as well as structural barriers that preclude entry into the animal or access to the target destination.
The patent describes a method for producing, and then delivering biologically active proteins to an animal using transgenic algae. The delivery of an antigen to an animal and activation of an immune response is offered as a specific example.
Infectious Disease in Humans
Infectious disease is an age-old problem. Early in human history, infectious diseases such as smallpox, bubonic plague, influenza, measles and many others caused epidemics and countless deaths. More recently, epidemics of Legionnaires' disease, human immunodeficiency virus, Ebola virus, Lyme disease, and others have been significant threats to human health.
Solutions to Infectious Disease
Early in human history, quarantine of infected individuals and improved sanitation measures were used to decrease the spread of infectious disease. Later, chemotherapeutic agents (drugs) were invented and, early on, included chemicals like sulfur and mercury. Modern chemotherapeutics include antibiotics, antiviral drugs, and antiparasitic drugs. Although essential, there are properties of such drugs that are not ideal. For example, drugs do not prevent disease. Rather, drugs are administered after a disease is diagnosed. Another problem is that infectious agents can develop resistance to the drugs such that the drugs are no longer effective against the infectious agents. Finally, drugs can cause serious side affects in the individual to which they are administered.
An alternative to chemotherapeutic agents is administration of immunogenic agents, wherein the immunogens that comprise a composition originating from the infectious agent whose infection one is trying to prevent. After administration, such immunogenic compositions preferably stimulate the immune system such that subsequent infection by the infectious agent is prevented, or disease symptoms caused by the infectious agent are decreased. Such immunogenic compositions are advantageous in that they are administered before the individual contracts the infectious agent. The stimulation of immunity in the individual caused by administration of the immunogenic composition, therefore, is designed to prevent infection and disease. Such immunogenic compositions normally produce few side effects in the individual to which the composition is administered. Finally, infectious agents do not normally develop resistance to immunity that develops as a result of administration of the antigen composition.
Infectious Disease in Non-Human Animals
Infectious diseases in non-human animals also cause significant morbidity and mortality. Such disease is important, not only because non-human animals can sometimes transmit the infectious agents to humans, but also because non-human animals and the products thereof are important human food sources and their loss is economically burdensome.
Infectious Diseases in Aquaculture
An example of an area where infectious non-human animal diseases continue to affect an important human food source is aquaculture. Aquaculture is the fanning of aquatic organisms, including fish and other seafood, for human consumption. Currently in the U.S., the domestic fishing industry meets only a small part of the total demand for fish. In 1997, for example, the federal trade deficit for imported fish was nearly $9 billion, the third largest component of the U.S. foreign trade deficit.
In an attempt to meet the demand for fish, the aquaculture industry has responded and, in 1997, produced over $55 billion in farmed fish (statistic from the Food and Agriculture Organization of the United Nations). Furthermore, the aquaculture industry has grown, historically between 10-20% per year for the last ten years. Therefore, it is clear that aquaculture is a rapidly emerging supplement and replacement for the traditional fishing industry and has tremendous growth potential.
One of the major constraints for aquaculture, however, is disease. Under the high density conditions under which fish and other aquatic organisms are farmed, the incidence of infectious disease can be high and, when disease does occur, it can spread rapidly through entire populations with high mortality. On average, 10-30% of farmed fish production, and up to 80% of shrimp production, is lost due to disease (Austin B., et al., 1987 Bacterial Fish Pathogens: Disease in Farmed and Wild Fish, 364 pp Publishers: (Ellis Horwood Ltd., Chichester, UK)).
Solutions to Infectious Diseases in Aquaculture
Again using aquaculture as a specific example, fish diseases with a bacterial etiology can be effectively treated with chemotherapeutic agents from the class called antibiotics. However, as much as 80% of the antibiotic may pass through the fish (Pothuluri, et al.,1998, Res. Dev. Microbiol 2:351-372), and development of bacteria resistant to the antibiotic may also arise. Such antibiotic-resistant bacterial pathogens can spread, creating entire fish populations harboring pathogenic bacteria that are resistant to the antibiotic. Clearly, it would be advantageous to prevent infection of the fish by the bacteria altogether. Another consideration is that viral and parasitic diseases cannot be treated with antibiotics.
Another strategy for preventing infection and reducing fish losses due to disease is prophylactic administration of an antigen composition, wherein the antigens are derived from an infectious agent, to stimulate the immune system of fish, other aquatic organisms, or other organisms generally (Gudding, et al.,1999, Vet. Immun. Immunopath. 72: 203-212).
Methods of Introducing Antigens into Animals
One problem with antigen compositions, especially in fish, is that many methods for administering them may not be technically or economically practical. For example, direct injection of the antigen composition into fish is labor intensive and is often expensive relative to the future market value of the fish. Furthermore, injection needles can cross-infect fish with contaminating infectious agents, and accidental injection of humans can cause severe infections and anaphylactic reactions. In addition, noninjurious injection of small fish may be difficult.
An alternative route of administration is an oral method wherein the antigen composition is incorporated into the fish food, for example. Another improved method of administering antigens to fish is immersion of the fish for a preset period of time in a suspension of the antigen. However, it can be costly to produce, purify, and package the antigens for such use. Prior art methods of producing antigens have involved the difficulty of growing fish viruses in culture systems to produce enough virus to obtain a sufficient quantity of antigen. In addition, antigen compositions to be administered orally are often encapsulated in expensive polysaccharide-coated beads. Finally, oral administration of antigen compositions have previously shown low and inconsistent levels of stimulation of the fish immune system, thereby minimizing protection against subsequent infection by the infectious agent.